Corrosion and stress corrosion behavior of CuCrZr alloy in high temperature pure water environment relevant to Japan's DEMO divertor

Abstract

CuCrZr alloy is one of leading candidate of the cooling system of the Japan's DEMO divertor. Proposals of operating conditions resembles in-service light water reactors hence underlines the importance of water chemistry. The latter significantly affects corrosion behavior. To understand CuCrZr alloy's corrosion behavior, several 500-hr static water corrosion tests with various water conductivity and water chemistries (including dissolved oxygen 100ppb respectively dissolved hydrogen 1600 ppb) at 230 °C pure water were conducted. Additional creviced bent beam (CBB) tests in degassed water and in water with dissolved hydrogen 1600 ppb at 230 °C up to 1000 h were also conducted to investigate stress corrosion behavior. Results showed that the weight loss of coupons tested in oxygen dissolved water was tenfold than that of in degassed water; and the loss in degassed water is twenty times higher than that of in hydrogen dissolved water. Presence of pure copper precipitates on coupons tested in hydrogen dissolved water suggests the occurrence of hydrogen reduction. In degassed water, the weight loss at high water conductivity (0.3 μS/cm) was close to that of low water conductivity (≦0.1 μS/cm), suggesting that the effect brought by water conductivity was smaller than the effect brought by different water chemistries. All CBB test coupons show no cracks. Relatively deeper metal dissolution induced etching at grain boundaries were observed comparing with those coupons from static water corrosion tests. Combined factors of tensile stress and metal dissolution lead to a speculation that stress corrosion cracking might happen under other aggressive environments or testing methods.